The presence and absence of solar energy has the potential to respectively raise and lower the internal temperature of a structure or housing. These effects are felt terrestrially in buildings and in vehicles over the course of a day, week or month. However, for spacecrafts outside the protection of the atmosphere heating and cooling can happen significantly faster and over a wider range of temperatures ranging from below −150° C. to above +150° C. in a matter of minutes. Internal temperature regulation is required to maintain a suitable operating environment for spacecraft subsystems. For example, it is preferable to maintain the internal temperature of a satellite in the approximate range of −10° C. to +30° C. to ensure effective operation of communication and control electronics, such as transceivers and processors. The aforementioned rapid and expansive external temperature swings must be accounted for when designing systems and devices for controlling the internal temperature of a spacecraft.
While smaller spacecraft are seen as one way in which current and future space science goals may be reached, the relatively low mass of such spacecrafts complicates the problem of temperature regulation. The relatively low mass of these spacecrafts means that they also have relatively low thermal capacitance, which makes them especially susceptible to wide temperature swings. Accordingly, thermal control is seen as increasingly important for smaller spacecrafts. However, smaller spacecrafts typically have short design cycles and are expected to be cost effective. Consequently, there is limited space and weight provided for temperature regulators such as heaters and thermal radiators.
Most spacecrafts rely on passive radiative surfaces to dissipate excess heat through thermal radiation into dark space. These types of passive thermal management systems typically employ thermal radiators that are sized for maximum power dissipation requirements. The thermal radiators typically include a coating with a fixed thermal emissivity value that is selected as a tradeoff between efficient heat dissipation at upper temperatures and sufficient heat retention at low temperatures.
In contrast active thermal management systems include some combination of electro-mechanical systems, heating and cooling pipes and/or voltage controlled variable emittance panels applied over thermal radiators. There are a number of problems associated with active thermal management systems including cost, complexity, size, weight, redundancy and the risk of catastrophic damage. The risk of catastrophic damage is exceptional in that such damage would occur in outer space where a satellite cannot easily be fixed, if at all. Thus, damage to an active thermal management system of a satellite may mean that the entire satellite is rendered inoperable.